Some more info would be helpful. What type and wattage of light are you using? Passive intake or fan powered? Avg room temps the grow box is going in? Are you worried about smell?
My grow box is basically a 3x3x3 cube. The actual grow area is 3 tall x 3 wide x 22.5 deep. The remaining 3x3x12.5 is a soundproof housing for my exhaust fan. I am using a 250w hps with active air 4in inline fan and carbon filtration. Passive intake is about 14in x 14in. In this setup I still wish I would have gotten the 6in inline fan, this summer with room temps avg. 78-84 my box temps soared and avg around 89-94. In the winter when room temps avg 68-72 box temps were a comfy 78-82.
Ventilation is one of the most important yet overlooked components of indoor growing. There are a number of really good threads on this site about venting and stealth growing. Post some more info and I will try to help if I can. Good luck.
